The all-American crew would consist of two people past childbearing age due to the radiation doses they would be exposed to by using current equipment. Technological constraints also dictate the number of people that could go on this mission, said Jane Poynter.

Poynter was one of the first Biosphere 2 crew members and is a co-founder of Paragon Space Development Corporation, which is developing the life-support system for the foundation's Mars mission. The foundation is also in talks with the National Geographic Society about a potential partnership on the mission.

While humans have a long history of setting off into the unknown on our own planet and in the immediate vicinity, space travel beyond low-Earth orbit and the moon—and what it means for the mental well-being of human crews—is a new frontier. (Read about risk takers in National Geographic magazine.)

"I think these will be bigger challenges than technology challenges," said Jason Kring, a researcher at Embry-Riddle Aeronautical University in Florida who studies how humans perform in extreme environments.

"Now fast forward to Mars—you can't talk to anybody in real time," said Kanas, who has studied psychological issues in astronauts for NASA.

"If you have a fire you have to deal with it yourselves," he said. "You can't evacuate anyone if they develop issues ... You're really isolated."

Isolation was the hardest part of living in Biosphere 2, a self-contained habitat meant to simulate Earth's various environments in the Arizona desert, said Poynter.

"We weren't as prepared as we should have been for being isolated," she said. Some of Biosphere 2's crew members developed depression or mood swings, and psychologists were brought in to help those individuals cope.

But the members toughed out their two-year stints, Poynter said, adding that she will advocate for the Mars crew to get training in how to deal with psychological challenges.

Mission planners will also be talking to NASA and to people who have spent extended periods of time at the ISS about how to plan for such hardship, she said.

Size Might Matter

Embry-Riddle's Kring and UCSF's Kanas both questioned the wisdom of the proposed two-person Mars crew.

"I think two is a setup for problems," said Kanas. "You can get along with anybody for a month, but you're talking about a year and a half or longer, and it's different."

Kring said that if the teammates got upset with each other, there would be no one to help smooth things over or take up any slack workwise.

There have been instances in the Russian cosmonaut program in which crew members in space got mad at one another and didn't speak for months, he said.

Crew members would be able to communicate with people on Earth, but interactions between crews in space and teams on the ground can develop their own set of problems.

Kanas's research has shown that crews in space will sometimes displace negative feelings onto ground teams. That can result in crews feeling like no one on the ground cares about them, he said.

Russian investigators have found that teams in space might also withhold some information from ground personnel, giving support personnel on Earth an incomplete picture of what's happening on the spacecraft, Kanas noted in an article published in 2010 in the Journal of Cosmology.

The Right Stuff

But experts say that some psychological issues can be avoided or mitigated with proper crew selection and training.

David F. Dinges, a psychology researcher at the University of Pennsylvania Perlman School of Medicine, thinks a two-person crew could work, depending on the people involved.

"It sort of depends on which two people and the nature of the habitat and the nature of what they have to do," he said.

There's no hard-and-fast list of characteristics that make a good crew member, said UCSF's Kanas, who has helped NASA screen astronaut candidates.

In general, good crew members are those who enjoy both working alone on projects and socializing, Kanas said.

This is so crew members can go off and give themselves and their teammates a break from each other, but then come together for meals or to work out a problem.

That helped to diffuse tensions that surfaced among a team that, even though they got along very well before they went inside, developed issues within days of starting their simulated mission, Kring said.

Audacity

It would be ideal if the Inspiration Mars Foundation's two-person crew were an attached couple, said Paragon's Poynter: "It's immeasurably helpful to have someone who you know and who you trust."

That setup would also help address any concerns of a romantic relationship developing between male and female crew members.

Poynter said she would love to go to Mars with her husband, former Biosphere 2 crew member and Paragon co-founder Taber MacCallum. "When we were in the Biosphere, we would sit on the beach," she said, "[and] just imagine ourselves hurtling towards Mars or being on the surface of Mars."